Safety circuit switch with a pneumatic time delay return



March 26, 1968 w, F, SCHULTZ 3,375,335

SAFETY CIRCUIT SWITCH WITH A PNEUMATIC TIME DELAY RETURN Filed Nov. 22,1965 I N VENTOR.

.'' ATTORNEY 3,375,335 Patented Mar. 26, 1968 3,375,335 SAFETY CIRCUITSWITCH WITH A PNEUMATIC TIME DELAY RETURN Werner 1F. Schultz, Flint,Mich, assignor to General Motors Corporation, Detroit, Mich, acorporation of Delaware Filed Nov. 22, 1965, Ser. No. 509,135 4 Claims.(Cl. 200-33) ABSTRACT OF THE DECLOSURE An electric switch which includesa fluid time delay return so as to remain actuated by a periodic motion.

My invention relates generally to a safety switch and more specificallyto a safety switch with a pneumatic time delay return so as to bemaintained in a closed position by periodic actuation. A nonlimitingexample of the utility of my invention is in connection with a pumpdriven by an electric motor. In such a system, it is desirable to shutdown the electric motor in case of a defect or mechanical breakdown inthe pump. One of the easiest ways of accomplishing this shutdown is toprovide a switch which can be actuated by a cam, eccentric or otherdevice on the pump motor combination which produces a periodic motion. Aproblem associated with the use of a periodic actuator, however, isthatthe actuator may stop in its extended position which would maintainthe switch closed even though the motor had stopped.

My invention then is specifically directed toward providing a switchwhich will be maintained closed by a periodic motion and which will openwhen this periodic motion ceases irrespective of the position of theactuator. In a broader sense, my invention is capable of use in anyapplication where it is desirable to provide a signal or a controlresponsive to a periodic actuating motion.

The exact nature of this invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the annexed drawing in which:

FIGURE 1 is a longitudinal cross section of a safety circuit switch witha pneumatic time delay return in accordance with my invention showingthe switch in its unactuated position.

FIGURE 2 is a section taken on a line 2--2 of FIG- URE 1 and looking inthe direction of the arrows.

FIGURE 3 is a view similar to FIGURE 1 showing the switch in its firststage of actuation with the switch in its switch open position.

FIGURE 4 is a view similar to FIGURE 1 showing the switch and the timedelay means fully actuated.

FIGURE 5 is a view similar to FIGURE 1 showing the switch maintained inthe switch closed position by the time delay means after the removal ofthe switch actuating means.

Referring to FIGURE 1 in detail, my safety switch comprises acylindrical housing 12 which has a somewhat recessed end wall 16provided with an aperture 18. The aperture 18 is closed by a one-wayflapper valve 20 mounted on the end wall by a snap ring 22 which isdisposed between the fiapper valve 20 and a circumferential bead 24 onthe end wall 16. A first piston 26 is slid-able within the cylindricalhousing 12 such that an air gap 28 is provided therebetween. Thereciprocable piston 26 and the housing 12 form a first chamber 30. Acoil spring 32 is disposed within the chamber between the end wall 16and the piston 26 to urge the piston toward the right as viewed in thedrawings. The piston 26 is hollow and has a second piston 34reciprocably disposed within it. Again an air gap 36 is provided betweenthe two pistons and the two pistons form a second chamber 38 with asecond lighter coil spring 40 disposed in this chamber. The spring 40urges the piston 34 to the right with respect to piston 26. An axiallyextending annular flange 42 extends from the forward face of the piston34 into the chamber 38. The face of the second piston 34 has an aperture44 closed by a one-way flapper valve 46 which is held against the faceof the piston by the coil spring 40. The piston 34 is also hollow andreceives a push rod 48. The first piston 26 has a cap member 50 whichabuts radially outwardly extending wings 52 formed by an enlargedforward portion 54 on the push rod and fixes the extreme right handrelative position of piston 34 with respect to piston 26. The cap member50 is a metallic conductor and bridges a pair of spaced contacts 56mounted within the cylindrical housing 12 to close a circuit when thepiston 26 is in the switch closed position. (See FIGURE 4). The righthand end of the push rod 48 extends through an annular boss 58 on thehousing closure cap 14 with a gap 59 therebetween and into abutment witha cam 60. The cam 60 is merely representative of any periodic motionactuation source. With the above-described structural details in mind,the operation of my switch will now be described.

As the cam 60 rotates from the position shown in FIGURE 1 to that shownin FIGURE 3, the push rod 48 and piston 34 will move to the left to theposition shown in FIGURE 3. This movement will be against the action ofthe light coil spring 40 and will compress the air entrapped within thechamber 33. The entrapped air thus compressed produces a differentialpressure across the piston 26 which causes it to move toward the leftagainst the action of coil spring 32. Continued rotation of the cam toits high point pneumatically moves piston 26 further to the left untilthe end wall of the piston 26 abuts the cylinder end wall 16. Thisleftward movement of piston 26 evacuates chamber 30 through the one-wayflapper valve 20 and the conductor cap 50 on piston 26 is moved to abridging position where it electrically connects the spaced contacts 56.The contacts 56 are on resilient arms 57 and the right hand ends of thecontacts 56 are ramped at the right hand ends 56' so that as theconductor cap 50 moves to its bridging position, the contacts 56 arespread radially. The contacts 56 then are biased radially inwardly intocontact with the outer circumference of the cap 50 in the switch closedcondition The relative position of the parts in my switch in thiscondition are shown in FIG- URE 4. While I have shown the above motionof the two pistons 26 and 34 in two distinct steps, it is to beunderstood that this was for purposes of clarity only. In actualoperation, the motion of the pistons occur simultaneously, however, inthe leftward or switch closed direction the motion of piston 34 lagsthat of piston 26 because of the spring forces. I

Referring now to FIGURE 5, as the cam continues rotation from its highpoint to the solid line position shown therein, the push rod 48 and theinner second piston 34 will move toward the right under the influence ofspring 40 and the pressure of the air entrapped in chamber 38. Thepiston 26, however, will remain in the left hand position where the cap50 bridges the contacts 56 because the chamber 30 is below atmosphericpressure. As the cam 60 rotates further to the dotted line position, thepush rod 48 and the piston 34 will not move further toward the rightbecause the wings 52 on the push rod 48 abut the cap member 50. Thisaction prevents the inner piston 34 from being withdrawn too far out ofthe outer piston 26. The time delay means just described is of limitedduration as air enters the evacuated chamber 30 through the longitudinalair gap 28 to increase the pressure toward atmospheric. As the pressurebuilds up, the differential pressure force across piston 26 whichopposes the force of spring 32 decreases. Before the pressure increasesto a point where piston 26 will have started to move toward the right,the cam 60 will have rotated back to the position shown in FIGURE 3 torepeat the actuation chain of motion as described above and thus theswitch is maintained closed. This action repeats itself as long as thereis a periodic motion actuating force acting on push rod 48.

When the reciprocating driver cam 60 stops, the switch will open afterthe limited duration of the time delay as described above. Should thedrive cam have stopped in the position of FIGURE 4 where the cam is inthe same position as shown in FIGURE 3, the push rod 48 and the piston34 will be held inwardly toward the left and chamber 38 is pressurized.The pressure in chamber 30 will increase to atmospheric, as before,because of air supplied through the gap 28. When this occurs, the forceof spring 32 is sufficient to move piston 26 toward the right againstthe force of spring 40 and the differential pressure force acting onpiston 26. The parts will then be as shown in FIGURE 3. Eventually, thepressure in chamber 38 will diminish to atmospheric because of itscommunication with the atmosphere through gaps 36 and 59. Upon renewedmovement of the cam 60 from the position of FIGURE 3 to the position ofFIGURE 1, the piston 34 will first be returned to its extreme right handposition. In this action, air is admitted to the chamber 38 via theoneway flapper valve 46. The switch then resumes the sequence asoriginally described.

Thus it can be seen that I have invented a safety switch which ismaintained closed by a periodic actuation and which will open uponcessation of the periodic actuation irrespective of the position of theactuator.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and that it isintended to cover all changes and modifications of the example of theinvention herein chosen for the purposes of the disclosure, which do notconstitute departures from the spirit and scope of the invention.

I claim:

1. An electrical switch comprising in combination, a closed cylindricalhousing having end walls, a pair of spaced fixed contacts resilientlymounted on said housing, said fixed contacts each having a ramp means, afirst hollow piston reciprocable within said housing and forming a firstchamber with one of said end walls, one-way valve means on said one endwall, a conductor on said first piston, said conductor bridging saidspaced contacts in one position of said first piston and abutting saidotherv 'end wall in a second position of said first piston, first springmeans in said first chamber urging said first piston toward said otherend wall, a second piston reciprocable in said first hollow piston andforming a second chamber therewith, second spring means in said secondchamber, second one-way valve means on said second piston, and rod meanson said second piston extending through said other end wall wherebymovement of said rod means toward said one end wall pressurizes saidsecond chamber to move said first piston and conductor to said oneposition camming said contacts into biasing abutment therewith andbridging said contacts, said first chamber being evacuated to delayreturn of said first piston upon depressurization of said secondchamber,

2. An electric switch comprising:

a first hollow piston,

a second piston reciprocably mounted therein,

a conductor carried by one of said pistons,

a housing including a cylindrical surface,

said one piston reciproca'bly engaging said cylindrical surface andforming a chamber therewith,

a fixed contact mounted on said housing so as to be spaced from saidconductor in a first position of said one piston and contacted by saidconductor in a second position of said one piston, said one piston beingmoveable to one of said positions by a fluid force created by movementof said other piston in a direction toward said one position, and

fluid time delay means including said chamber which is exhausted bymovement of said one piston to said one position, said fluid time delaymeans delaying the movement of said one piston away from said oneposition after movement of said other piston in a direction away fromsaid one position whereby said switch is adopted to be actuated by aperiodic motion.

3. The electric switch as defined in claim 2 which further includesa'first spring means between said pistons urging said pistons away fromeach other, and second spring means between said housing and said onepiston urging it toward said other position, said first spring meansbeing lighter than said second spring means.

4. An electric switch comprising,

a housing including'a cylinder with an end wall,

a first hollow piston,

a second piston reciprocably mounted within said first piston forming afirst chamber, a first one-way valve opening into said'first chamber,one of said pistons reciprocably mounted within said cylinder forming asecond chamber,

second one-way valve opening out of said second chamber,

a pair of contacts carried by said housing,

a conductor carried by said one piston, said conductor spaced from saidcontacts in a first position of said.

one piston, and bridging said contacts in a second position of said onepiston,

first resilient means in said first chamber biasing said pistons awayfrom each other, and

second resilient means in said second chamber biasing said one pistontoward said first position whereby said one piston is moved from saidfirst position to said second position by movement of said other pistontoward said second position, said movement exhausting said secondchamber and delaying the return of said one piston to said firstposition after said other piston reverses direction whereby said switchis adapted to be closed by a periodic motion.

References Cited UNITED STATES PATENTS Re. 25,631 8/1964 Forwald 200-821,954,427 4/1934 Platz 20082 BERNARD A. GILHEANY, Primary Examiner.

F, BELL, Assistant Examiner.

